2-Benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one is known to have excellent interleukin-1β production inhibiting effect and to be useful as preventives and therapeutics for immune system diseases, inflammatory diseases, ischemic diseases and the like (JP-A-12-198776). However, this compound is a drug having extremely low solubility in water and is poor in its dissolution from preparations. There is, accordingly, an outstanding demand for an improvement in its dissolution.
As methods for improving the dissolution of extremely poorly water-soluble drugs, techniques such as the micronization of the drugs and the preparation of derivatives of the drugs are known. Concerning extremely poorly water-soluble drugs such as 2-benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one, however, micronization cannot improve their dissolution, and their conversion into derivatives leads to changes in drug activities and therefore, is not preferred.
Also proposed as methods for making improvements in dissolution include a method which comprises treating a physiologically active substance such as nifedipine with carbon dioxide, which is in a supercritical state or subcritical state, or with liquid carbon dioxide (for example, JP-A-2002-302435). These methods can improve the dissolution of slightly water-soluble drugs such as nifedipine, but cannot improve the dissolution of extremely poorly water-soluble drugs such as 2-benzyl-5-(4-chlorophenyl)-6-[4-(methylthio)phenyl]-2H-pyridazin-3-one.